offscreen: Fix possible infinite recursion when cloning
offscreen: Fix possible infinite recursion when cloning

There was a check previously for this, but it didn't catch all cases. This
one does.

clutter-project/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx